1. Field of the Invention
The present invention relates to a liquid crystal display device using a direct backlight device having cold cathode fluorescent lamps which is arranged on a back-surface side of a liquid crystal display panel and radiates light-source light to the liquid crystal display panel, and more particular to the arrangement structure of a plurality of cold cathode fluorescent lamps which is arranged in the inside of the backlight device.
2. Description of the Related Art
Recently, a liquid crystal display device has been popularly used as a display means for various information-terminal-use monitors including a personal computer, a mobile phone or a television receiver set or the like. In such a liquid crystal display device, an electronic image which is formed on a liquid crystal display panel is visualized by radiating light to the electronic image. With respect to miniaturized information equipment, there has been known information equipment which adopts the structure in which ambient light is utilized as a light source for visualization. However, to enable viewing of a favorable image on a relatively large-sized screen irrelevant to a condition of ambient light, many information equipment adopt the constitution in which an illumination light source is provided to a liquid crystal display panel, and an electronic image formed on the liquid crystal display panel is illuminated by illumination light radiated from the illumination light source.
With respect to the miniaturized liquid crystal display device, there has been known a liquid crystal display device which has the structure in which a so-called front-light device is arranged on a front surface of a liquid crystal display panel or in the vicinity of a periphery of the liquid crystal display panel as an illumination light source. However, with respect to a notebook-type personal computer, a computer monitor, a television receiver set or the like, an illumination light source which is arranged on a back-surface side of a liquid crystal display panel and is referred to as a backlight device has been adopted.
The backlight device is roughly classified into two kinds of backlight devices. One kind of backlight device is a side-edge-type backlight device which is used in a notebook-type personal computer or a computer monitor whose equipment size in the depth direction is limited, and another kind of backlight device is a direct backlight device which is used in a relatively-large-sized computer monitor or a television receiver set which is required to satisfy a demand for higher brightness and is arranged directly below a back surface of a liquid crystal display panel.
In these backlight devices, a cold cathode fluorescent lamp is mainly used as an illumination light source in many cases. The side-edge-type backlight device which uses the cold cathode fluorescent lamp is constituted by arranging the cold cathode fluorescent lamp on a side of a light guide body arranged on a back surface of the liquid crystal display panel and hence, the side-edge-type backlight device has an advantage that the backlight device can have the relatively compact constitution. However, the side-edge-type backlight device has a disadvantage that light utilization efficiency is low. On the other hand, the direct backlight device is constituted by arranging a plurality of cold cathode fluorescent lamps parallel to each other on a back surface of a liquid crystal display panel without arranging a light guide body and hence, the direct backlight device has an advantage that the direct backlight device can acquire high light utilization efficiency. However, the direct backlight has a disadvantage that a thickness of the backlight device per se becomes large.
For example, JP-A-2002-82626 (Patent document 1) discloses a backlight device which is constituted of a plurality of straight-tube-type fluorescent lamps as a light source, a light diffusion plate which is arranged on a liquid-crystal-display-panel side of the respective cold cathode fluorescent lamps, a polarization conversion film, a prism sheet, and a reflection plate which is arranged on a back-surface side of the respective cold cathode fluorescent lamps. Further, for example, JP-A-6-75216 (Patent document 2) discloses a liquid crystal display device which is configured such that such a backlight device is arranged on a back-surface side of a liquid crystal display panel and light-source light of the backlight device is radiated to a back surface of the liquid crystal display panel.